A commercial annular scintillation camera was purchased and a multiple pinhole collimator array fabricated to create a single photon emission computed tomography (SPECT) scanner for mice. The eight-hole collimator array will be rotated mechanically inside the annular scintillation crystal while projecting eight magnified images of the mouse onto the crystal. This scheme will allow an eight-fold improvement in sensitivity compared to a single pinhole and will allow complete projection sets to be acquired in a very short time. This system is now being mechanically assembled and the calibration and image reconstruction software are being written. An advanced signal-processing package was designed to acquire and process data from the Hamamatsu flat panel position-sensitive photomultiplier tube (PSPMT). This tube offers a number of advantages over competing PSPMTs in small animal PET applications but is subject to the degrading effects of pulse pile-up at high rates due to its large field-of-view (48 mm x 48 mm). Each analog/digital acquisition package, one for each tube, is designed specifically to minimize this effect while retaining the advantages of a large field-of-view. Several of the IC boards for these packages have been fabricated and tested and work on the digital elements of the package are now underway. During this reporting period the Imaging Physics Laboratory also supported the work of multiple intramural research groups in PET imaging studies of tumor hypoxia in mice, gene expression in mice, cerebral stimulation studies in the rat, quantitative methodological validation studies in the rat and mouse and a variety of other biodistribution imaging experiments. Modification and changes to the software of the ATLAS small animal scanner continued to be made in response to requests from these investigators and to enhance the functional capabilities of the system.